Anecdotal evidence suggests the existence of large differences among wild rainbow trout populations in growth, maturity, and mortality rates for reasons which are unclear. To determine the extent and nature of these differences, estimates of the density, length, age, maturity, and fecundity were made from each of 37 remote, wild, closed rainbow trout populations. An evaluation was made of i) the extent of among-population differences, ii) whether consistent tradeoffs occur among these population-descriptors, and iii) whether environmental variables of expected importance (such as littoral refuge, proportions of stream spawning to adult-lake area) could be used to predict, and provide possible explanations for observed among-population differences. Large differences exist among populations in rainbow trout fork lengths at age-2 (avg. age at first maturity), from 16.4 cm to 32.7 cm, and in natural mortality rates (0.48/yr to 1.51/yr). Results will be discussed from: i) tests of published theoretical and empirical models of potential tradeoffs among growth, maturity and mortality of salmonids and other fishes and ii) predictions of among population differences in growth, maturity, and mortality rates, each, using environmental variables.